Black Hawk helicopters get a giant bath

Ten Black Hawk helicopters were submerged in a sea of foam within minutes after a worker accidentally triggered a US military hangar's fire alarm.

Aerial footage of the scene showed the convoy – seven parked in the hangar and three on the ramp outside – buried in the fire suppression foam at the Oklahoma Army National Guard base in Tulsa Tuesday morning.

Only one of the base's 11 Black Hawks escaped the foam, which in some parts was more than four metres deep, according to pilot Will Kavanagh.

"It's hard to get to the shut off valve when you have 15 feet (4.5m) of foam in the hangar," Mr Kavanagh told Osage SkyNews 6 HD.

"Imagine being in the middle of the foam and trying to find your way around.

"It's like being in a fog bank without being to see in front of you."

Complicating the process was a mini-tornado that threw the foam into the air as it passed.